dict1 = {"k1": "v1", "k2": "v2", "k3": "v3"}
for x in dict1.keys():
    print(x,end=" ")
for y in dict1.values():
    print(y,end=" ")
print()
for a, b in dict1.items():
    print(a,b)
dict1.update({"k4":"v4"})  # 使用update无返回值

for a, b in dict1.items():
    print(a,b)

del dict1["k1"]
print(dict1)
print(dict1.pop('k5',None))

print(dict1["k2"])
print(dict1.get("k6", None))
